Automatic sound control



July 16, 1963 w. B. WADSWORTH AUTOMATIC SOUND CONTROL Filed Sept. 15,1958 FlGl FIGZ 7 OUTPUTC SAMPLING AND common. DEVICE AMPLIFIER I QRIABLE D E F AMPLIFIER AMPLIFIER SAMPLING MICROPHONE RECT'F'ER B c: T a 73i 4 R: Er J C, PH/T 4 l f A E7 K; a, 0

INVENTOR 4414;? W

ATTORNEY United States Patent "ice 3,098,121 AUTOMATIC SOUND CONTROLWilliam B. Wadsworth, Concord, Mass., assignor to David Clark CompanyIncorporated, Worcester, Mass., a corporation of Massachusetts FiledSept. 15, 1958, Ser. No. 761,217 1 Claim. (Cl. 179-1) This inventionrelates to a unique application of automatic control of sound in a noisylocation. The prior art utilizes the principle that where a publicaddress system is used in a noisy location, a constant signal to noiseratio can be approximated if a sampling microphone is used to produce acontrol signal for the amplifier in the public address system, wherebythe sound power output is increased in proportion to the increase in thelocal interfering noise. A fundamental difiiculty lies in the fact thatthe sampling microphone picks up both sound and desired signal, and somedifferentiating means is required. Many schemes have been proposed inthe prior art with varying success.

In the present invention this problem does not exist over the range ofsound signal required, and therefore this invention is simple and moreeffective. The principal application for this new method is in noisyenvironments where the operator is using earphones such as in jetairplane ground crews, etc., Where a desired signal or sound istransmitted to the listener through the earphones which are themselvesshielded from the ambient noises by means as described in prior pendingapplications, erg, S.N. 597,161, filed July 11, 1956 and 603,111 filedAugust 9, 1956, now Patent Numbers 2,899,683 and 2,981,958 respectively.

The principal object of the present invention resides in the provisionof devices such as ear protectors, including earphones, which areadapted to protect the ears of the user from a high noise level which isnot desired to impinge upon the ears of the user, and including asampling device and an electronic control for the loudness of the signalimpressed upon the earphones. The sampling device samples the ambientlocal surrounding atmosphere for increase and decrease in unwantedsounds, and the electronic system is controlled by the sampling deviceto increase and decrease substantially proportionately the ear phonesignal in the ear protector, whereby the user automatically hears wantedsignals from a distance at approximately the same sound level regardlessof the increase and decrease in the unwanted loudness of the sound levelsurrounding the user and the earphones which he is using.

Other objects and advantages of the invention will appear hereinafter.

Reference is to be had to the accompanying drawings, in which FIG. 1 isa view illustrating the present device;

-FIG. 2 is a diagrammatic view showing the system; and

FIG. 3 is an electronic diagram showing the details of the system.

In carrying out the present invention, there is provided a set of earprotectors which may be such as are described in copending applicationSerial No. 495,394, filed March 21, 1955, now Patent No. 2,946,862.These ear protectors are provided with phones 12, 12. These phones andear protectors are not a part of the present invention except as part ofthe combination, and it is believed that they do not need to he furtherdescribed. However, these earphones are connected into the sampling andcontrol device which is indicated in this case as being in a housing 14and may be mounted on the headband 16, 16. The sampling device isprovided with a sampling microphone and it is to be understood that thewanted signal feeds into the ear protector by well known means, andthence feeds to the earphones, so that the user receives all his I 341925,121 Patented July 16, 1963 information from a remote point while hisears are at the same time effectively protected against the deleteriouseffects of high sound energy existing locally in the atmospheresurrounding the user. In this way the operator is apprised ofinformation he needs in spite of the high level of noise surroundinghim.

Referring now to FIG. 2, it will be seen that the speech input ordesired signal is impressed upon amplifier A which then is transferredto the variable gain amplifier B and thence to the speech output at Cwhich is of course the earphones 12. Without the present invention, theloudness of the speech output at C (or earphones '12, 12) depends onlyon the origin of the signal, and the signal level to the user thereforedepends solely on the ambient noise level. Total signal-to-ambient-noiseratio tends to rise and fall, making for less intelligible speech, inthe absence of means for causing the loudness of the speech output torise and fall with the rise and fall of the ambient noise.

The sampling microphone is shown as at D in the diagram of FIG. 2, andalso in FIG. 1. This microphone is in constant communication withamplifier E and this microphone signal is then transferred to therectifier P which then controls the variable gain amplifier B toincrease or decrease the level of loudness and speech output at C,depending upon the signal received by the sampling microphone at C.

A circuit for carrying out this effect is shown in FIG. 3 wherein theconnections are as indicated and the various elements are as follows:

Also affects It is believed from the foregoing that the use andoperation of this invention will be apparent. The device provides anautomatic amplifier for desired signal which is to be impressed on aprotected ear-phone from a remote point, whenever the noise levelincreases in the surrounding atmosphere as respects the user of thedevice. Therefore regardless of the ambient noise level, the desiredsignal through the ear-phones comes in on a level which is intelligibleto the operator at all times. The strength of the signal at theear-phones can be varied by varying the values of portions of thecircuit but in general the variation of increase of signal at the phoneswill be more or less proportional to the increase in ambient noise levelalthough this proportion may be varied to suit special conditions.

Having thus described my invention and the advantages thereof, I do notwish to be limited to the details herein disclosed, otherwise than asset forth in the claim, but what I claim is:

Audio communication apparatus with volume control operated by ambientnoise; comprising in combination an ear protector shell adapted to beapplied to the head of a user against the users ear, support means forretaining said shell in position on the users head, said shell havingrelatively high attenuation of exterior sound Waves and ambient noise, atransducer mounted in said shell for communicating wanted sound to theusers ear as the function of an electrical signal applied to thetransducer, means for picking up wanted sound and transforming the sameinto an electrical signal, a variable gain amplifier connected to saidWanted sound pick up means and to said transducer for applying to thelatter a signal of a variable gain, a sampling microphone mounted onsaid support means for picking up unwanted ambient noise, second amplifying means connected to said microphone, and recti- References Citedin the file of this patent UNITED STATES PATENTS 2,501,327 Good Mar. 21,1950 2,891,116 Nichols June 16, 1959 2,946,862 Wadsworth et a1. July 26,1960 2,972,018 Hawley et a1 Feb. 14, 1961 OTHER REFERENCES ElectronicControl of Noise Vibration and Reverberation, by Olson, Journal of theAcoustical Society of America, vol. 28, No. 5, September 1956 (Reprintby RCA Labs).

